As the biotechnology has been developed, a flow cytometer is more commonly used in the fields of medicine and biology for automatic analysis and fractionation of cells or chromosomes (which are referred to simply as “cells”). The flow cytometer forms a stream of the analyte cells within a flow channel performing as cell aligning means, and irradiates laser beam on the stream of the cells to detect information light emitted/scattered at the cells (forward-scattered light, fluorescent/side-scattered light) Also, it converts the information light into electrical signals to analyze the cells based upon the electrical signals, allowing high throughput of analyzed cells and extraction (sorting) of a particular group of cells, if necessary.
FIG. 12 is a schematic view of the flow cytometer, illustrating a typical structure and operation thereof. In the flow cytometer shown in the drawing, a liquid suspension 201 containing cells received in a container and a sheath fluid 202 received in another container are guided into a funnel-shaped flow chamber (nozzle) 204 by air pumps 203. In the flow chamber 204, the sheath fluid 202 forms a cylindrical laminar flow, i.e., a sheath flow, encompassing the liquid suspension 201 therein, in which a discrete one of the cells runs one-by-one along the central axis of the flow chamber 204. Where the sheath flow is faster as closer to the bottom end of the flow chamber 204, laser beam 207 is irradiated from a laser beam source 205 and focused by a collective (focusing) lens 206. Most of the cells in the liquid suspension 201 are fluorescently labeled with fluorescent material such as a fluorescent pigment and a fluorescent-labeled monoclonal antibody. Therefore, irradiation of the laser beam onto the cells causes the scattered light and the fluorescent light.
The scattered light passes through collective optics including a collective lens 208 and a beam block 209 to an optical detector 210 such as a photodiode designed for detecting the scattered light. As to the fluorescent light, red-based fluorescent light is received through another collective optics including a collective lens 211, a half-mirror 212, a collective lens 213, and a filter 214 by an optical detector 215, also green-based fluorescent light is received through the half-mirror 212, a collective lens 216 and a filter 217 by an optical detector 218. Photomultiplier tubes are typically utilized as the fluorescent detectors 215, 218 capable of detecting faint fluorescent light. A signal processing circuit 219 receives various signals output from the detector 210 for the scattered light, the detector 215 for the red-based fluorescent light and the detector 218 for the green-based fluorescent light, and analyzes strength of the scattered light and the fluorescent lights, thereby to identify the analyte cell.
As above, the conventional flow cytometer is designed such that the optical detectors 215, 218 detect the scattered light and fluorescent light that are collected by the collective optics including the collective lens 211, the half-mirror 212, the collective lens 213, and the filter 214. Also, the collective lens 211 collimates the fluorescent light scattered at each of the cells running one-by-one along the central axis of the high rate flow in the chamber. (See, for example, Japanese Laid-Open Patent Applications JPA 59-000643, JPA 59-184862, JPA 60-195436, and JPA 03-503808.) However, the particles may be stuck at the orifice of the flow chamber 204, or the flow may be disturbed or inclined. In those cases, while the flow chamber 204 has to be removed from the system and cleaned, the optical alignment (including, for example, an irradiation position and a focal length of the laser beam, a position and an angle of a nozzle, an irradiation position and a focal length of the objective lens) must be adjusted, such adjustment task is considerably cumbersome and complicated. Also, it is difficult to downsize the optics used in the system since those lens incorporated therein have a high aperture ratio.
To address the above-mentioned drawbacks, an approach for optical detection at a given flow path in the flow cell (flow chamber) has been proposed, in which the collective lens with the high aperture ratio is attached onto the flow cell, for collecting the fluorescent light from the cell. However, such a small lens cannot collimate the fluorescent light sufficiently. Also, multiple collective lens often have to be combined in many cases, therefore, improvement of sensibility cannot be expected because of air layers interposed between the adjacent lens. To this end, it was impossible to downsize the optics of the system.